On Sun, 12 May 2013 17:56:21 -0400, "Ralph Mowery"
wrote:
"Jeff Liebermann" wrote in message
.. .
On Sun, 12 May 2013 16:34:53 -0400, "Ralph Mowery"
wrote:
"Jeff Liebermann" wrote in message
...
Yes, I know. A clean workbench is a sign of a sick mind.
http://802.11junk.com/jeffl/pics/home/slides/chain-saw-repair.html
It's currently not quite as messy, but it's close.
Looks like you have an antenna harness for phasing 2 meter antennas.
I guess you mean the Wilkinson power divider/splitter in the lower
left. It's not for phasing antennas, but for combining the signals
from two receive only 1090MHz antennas for ADS-B reception. The lines
are 3/4 electrical wavelengths long RG-6a/u because I couldn't find
any small diameter 75 ohm coax. That was a prototype I just threw
together to see if I really needed the 100 ohm resistor for receive
only. With low gain antennas, it's not needed. For high gain, where
impedance matching is more important, it's needed.
I know about the Wilkinsson devider. Not sure if it is done now, but the
CBers would put two antennas on their cars and especially the big trucks.
Feed them with a T and 1/4 wavelengths of coax if I recall corectly.
Yep. It was called a "co-phasing harness". Basically, the same thing
as a Wilkinson power divider. The original purpose was to deal with
the problem that the truckers were having with mounting antennas on
their big rigs. The antenna could not be mounted on top of the
tractor or trailer because the weight scale operators did not like
antennas smashing into the overhead clearance gauges. However, one
antenna on the side of the tractor didn't work very well because it
blocked signals on the other side. Two antennas were just fine. The
only problem was that while in receive, there was little loss from
either antenna, in transmit, the power was split equally between
sides. To compensate, doubling the transmit power was deemed
necessary. It worked.
At the time 1973(?), I was working on an ill fated CB related project
that would eventually have Antenna Specialists' name on it. I
discussed the co-phasing harness problem with one of their engineers.
He mumbled something about it being a great way to double antenna
sales. The rest you can guess.
Thought you were going to do that to the chain saw for 2 meters to help out
your handy talkey while sawing wood. As if you could hear it over the
noise.
Yacking on the radio while operating a rather dangerous piece of
machinery is not a great idea. If someone wants to yell at me, they
can wait until I'm done sawing.
I have not looked over the power devider in a long time. I was thinking the
100 ohm resistor was mainly to absorbe the unballanced power. If everything
was matched you could leave it out, but as you well know, nothing is perfect
in the RF world.
True for a splitter. Not quite so true for a combiner. It's main
purpose it to provide the best possible isolation between input ports.
The phase shift through the *TWO* 1/4 wave lines, combined through the
100 ohm resistor, exactly cancel, which provides the necessary
isolation. If you look at the specs for a combiner, you'll see the
isolation specification.
What are you using for a receiver for the ADS-B ?
One of the receive stations for one of the aircraft monitoring
networks.
http://planefinder.net
http://my.pinkfroot.com
http://Flightradar24.com
I have one of the dongles
that plugs into the usb of a computer on order. Should be here Monday. It
tunes from about 25 MHz to over 1 Ghz from the writeups. Off ebay here is
the item number.
310655269457
I don' t see how they can make and ship a device like that for only $ 11.00.
Yep, very cheap. I couldn't afford to ship an empty box for that
price.
http://www.ebay.com/itm/310655269457
There are numerous projects on the web for turning it into everything
from a spectrum analyzer to a radio scanner.
http://www.hamradioscience.com/building-an-inexpensive-ads-b-receiving-and-sharing-station/
http://panteltje.com/panteltje/xpsa/index.html
I could use one of those RTL8232U dongles, but I have a different
problem to solve. 1090MHz is in the middle of the frequencies used by
DME (distance measuring equip) which provides a challenge in
interference reduction using DSP. The receivers will probably be
located in the middle of transmitter infested mountain tops, which
means they need a really good IM tolerant front end. The antenna
problem is also unique in that it requires maximum gain toward the
horizon in order to maximize range, but also must still have some gain
overhead to hear closer aircraft. I combine two antennas for the
purpose.
http://802.11junk.com/jeffl/antennas/AMOS-3-INV-1090Mhz/index.html
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558